Field of the Invention
This invention relates generally to the deposition of thin film materials, and more particularly, a high efficacy multi-layer seal structure formed on an organic light emitting diode (OLED) device and the process for depositing the same.
Description of the Related Art
OLEDs are solid-state devices composed of thin films of organic molecules that create light with the application of electricity. OLED technology is used in commercial applications such as displays for televisions, mobile phones, portable digital media players, computer monitors, car radios, and digital cameras. OLED devices provide brighter, crisper displays on electronic devices and have lower power requirements than conventional light-emitting diodes (LEDs) or liquid crystal displays (LCDs).
An OLED device typically includes a stack of thin layers formed on a substrate. In the stack, a light-emitting layer of a luminescent organic solid, as well as adjacent semiconductor layers, is sandwiched between a cathode and an anode. The light-emitting layer may be selected from any of a multitude of fluorescent organic solids. Any of the layers, and particularly the light-emitting layer, may consist of multiple sublayers.
In a typical OLED, either the cathode or the anode is transparent. The films may be formed by evaporation, spin casting, other appropriate polymer film-forming techniques, or chemical self-assembly. Thicknesses typically range from a few monolayers to about 1 to 2,000 angstroms. OLED devices are extremely sensitive to moisture and susceptible to water damage. Water can instantly damage the organic materials of the displays and significantly shorten the operational lifetime of the device. Therefore, improved sealing processes are important for practical manufacturing.
Currently, protection of OLED against oxygen and moisture can be achieved by encapsulation of the device. The encapsulation can be obtained by means of a single thin-film layer situated on the substrate, surrounding the OLED. Thin film encapsulation is used to prevent moisture in top emitter OLED devices because of their general transparent attributes. There are various methods of thin film encapsulation that exist today. One such approach is to encapsulate the OLED with a multi-layer barrier structure using inorganic and organic layers. Another method disclosed in U.S. patent application Ser. No. 14/203,426, describes a process for encapsulating semiconductors by the deposition of multi-layer barrier structures using organic, inorganic and metallic layers.
Though various layers have been incorporated into the encapsulation structures above, each of these layers have some level of permeability to the environment. As such, the efficacy and reliability of these sealing methods are unfavorable.
Another method for encapsulation involves sandwiching the OLED between two glass panels and sealing the edges. Perimeter epoxy seal is traditionally used with a glass or metal cover provided in the back of the display with a large amount of desiccant. However, this method is only available for bottom emitter OLED devices. In top emitter OLED devices, light is required to travel through the glass cover, and therefore there is no room for the application of desiccant.
While these methods may be suitable for the particular purpose employed, or for general use, they would not be as suitable for the purposes of the present invention as disclosed hereafter.
It is, therefore, a primary object of the present invention to provide a high efficacy seal structure for OLED devices that acts as a moisture barrier.
It is another object of the present invention to provide a seal structure including the process for depositing several layers of transparent inorganic dielectric materials on the OLED device.
It is another object of the present invention to provide a transparent multi-layer seal structure capable of being used with top emitter OLED devices.
It is another object of the present invention to provide a multi-layer seal structure capable of being repeated several times to form a thicker transparent seal.
It is another object of the present invention to provide an improved method for depositing a multi-layer seal structure on an OLED using ALD and sputtering techniques.